I met [producers] Joel Silver and Susan Downey in the summer, and there was interest at that point. There seemed to be sort of two ways of going with it. There was obviously, as there always is in this business, there was interest in getting another star for the marquee, and all these wonderful names were being batted around. And there was another feeling that it might be better to have a character actor play the role, so that you just experience the character and you weren’t looking at somebody going, "Oh look there’s somebody really famous playing the part."

They just wanted to experience the character. So there was a creative discussion that went on for quite a long time amongst the powers that be. And it was in those sort of things of, "They’re interested, oh it’s gone away, it might be coming back, oh they’re interested again, oh no it’s gone again," that went on for a long time. And then I happened to be in Switzerland with a group of friends and I suddenly got a phone call saying, "If you can get to London tomorrow and meet [director] Guy [Ritchie], they’re interested again." So I flew to London and auditioned for Guy.

Though he only appeared in two of Sir Arthur Conan Doyle's stories — 1883's "The Final Problem" (which ended with Holmes and Moriarty falling to their deaths) and 1915's The Valley of Fear, Doyle's final Sherlock Holmes novel — Moriarty is the iconic Sherlock Holmes villain. While Harris admits that he "wasn’t tall enough and probably old enough" compared to the literary version, he also didn't want his Moriarty to be a reprieve of the version Eric Porter played in the second season of the British TV series, The Adventures of Sherlock Holmes.

Well you want to craft your own version but you also need to be in the same genre of film as everybody else, and you wanna stay true to, as they have with the series, to the spirit of Sherlock Holmes whilst making the character into sort of a, it’s like a superhero movie, it’s slightly in that genre of films, he doesn’t have any superpowers except he’s got a super intellect.

So we went back and forth about trying to come up with a look, and I was given a lot of input into how I wanted to look. There was a certain amount of thrashing around in terms of the character itself, with Robert [Downey Jr.] and with Guy, and all the people involved in creating the series.

I think that for me — and this is again my rational, it’s never explained in the story and I don’t really think it needs to be — but for me, the character’s amoral. He’s moved beyond the concept of there being a heaven and a hell and a God and a devil, and there being good and evil, he doesn’t believe in it. And if you don’t’ believe in that moral construct, then everyone is free to do whatever they want. He sees that whole approach to viewing the world and everything around them as being a childish construct. He doesn’t believe in the whole idea of there being good and evil, so he couldn’t conceive himself as being either good or evil. He’s just doing what’s good for him. It’s like asking, if you’re a fish, how could a fish conceive of space? You swim in the water that you swim in or the atmosphere that you’re in. For him it just doesn’t exist. The whole idea doesn’t exist.

Sherlock Holmes: A Game of Shadows was written by Kieran and Michele Mulroney (Paper Man), and follows Holmes (Downey Jr.) and Dr. Watson (Jude Law) as they try to take down Moriarty (Harris) with the aid of Holmes' brother Mycroft (Stephen Fry) and a gypsy named Sim (Noomi Rapace).